The formation of a new diploidal organism is preceded by a series of mutual interactions of haploidal gametes. This process is very complicated and requires the prior activation of reproductive cells. Male gametes eventually mature in the female reproductive tract, acquiring mobility and fertilization. This process takes place in two stages. Sperms are first capacitated. This phenomenon is reversible and leads to structural, cytophysiological and biochemical changes in the sperm plasma membrane as well as to the sperm hyperactivation. Then, due to the contact with the zona pellucida of the oocyte, the irreversible acrosome reaction occurs. This process involves the fusion of the sperm plasma membrane with the outer membrane of the acrosome, the release of enzymes and exposure of the inner acrosome membrane. This enables sperm to penetrate towards the perivitelline space and oolemma. Contact with the oocyte initiates a series of interactions leading to egg activation and the fusion of gametes. Each of these stages involves many different factors that result in the recognition, attraction and adhesion of reproductive cells. Knowledge about the activation mechanisms can improve the effectiveness of supported and controlled reproduction techniques